The present invention relates to a non-circular front chain wheel for crank gear.
It mainly concerns the cycle industry but may also find applications in other fields, such as physical exercise apparatus for body-building or rehabilitation, and in general, all apparatus using cycling motion and a chain or belt transmission system between the front wheel or wheels of the crank gear and one or a plurality of pinions actuating the device to be driven.
In apparatus of this type, the load moment, or in other words, the force exerted by the chain on the front chain wheel of the crank gear can be thought to be substantially constant, whereas the driving torque produced by the cyclist, is variable by nature, passing cyclically from a lesser value at the upper and lower dead points when the arms of the pedals, or the cranks, are aligned with the saddle and the axis of the crank gear, and a maximum value when the arms are substantially horizontal.
For obvious reasons of ease, most often circular front chain wheels are used, resulting in numerous disadvantages:
Shocks, stress, speed variation, loss of power at the upper and lower dead points and loss of power, causing an increase in cardiac rhythm, PA1 Substantial start-up effort when the pedal is on top, PA1 Pedalling effort depends on the sine of the angle of the pedal arm with the axis of the dead points, and is not a function of human ability, PA1 Cycling motion is not synchronous with natural effort, resulting in disproportionate muscular, tendon and joint efforts, thereby limiting performance as well as pleasure, PA1 Lack of motor function in all-terrain cycling due to drive torque variations, PA1 Necessitates rapid increase in rotational capacity to avoid muscular overload, which results in energy loss in the dynamic effects on the legs, PA1 Loss of energy in the crank gear axis due to the radial components of the effort provided by the cyclist, PA1 Acceleration is not in proportion with the effort communicated to the pedal, PA1 The related muscles, tendons and joints work in a jerky manner and are subject to substantial variations in effort. PA1 muscle force, tendon and joint resistance, PA1 geometry of the man-machine assembly, PA1 speed and acceleration of the vehicle and of the cycling motion, PA1 necessary moment, PA1 muscle sensation, PA1 type of pedalling desired.
A number of efforts to improve crank gear functioning have been suggested. For example, FR 83 09 015 describes an elliptical front chain wheel for a crank gear whose biggest radii correspond to the dead points. The foremost objective of this device is to obtain greater speed, but as it does not take into account muscle characteristics, it results in an increased variation in the efforts to be provided and increased tiredness, without, however, obtaining satisfactory results.
DE-A-3 709 482 and DE-U-8 522 573 also describe non-circular front chain wheels. These documents may seem to represent a slight improvement from the energy point of view, but by virtue of their geometry, do not enable the load moment of the front chain wheel to correspond with the potential possibilities of muscular forces that inherently characterize human anatomy.